1. Field of the Invention
This invention relates to communication systems, more particularly, to transmission of communication signals between a base station and a radiation element.
2. Description of the Related Art
A communication system typically includes multiple devices, such as equipment and cables, that may be located remote to each other. For example, FIG. 1 illustrates an example of a conventional communication system. A radio base station 102 may receive, and transmit, a plurality of communication signals for many different sources. For example, the radio base station 102 in FIG. 1 may send and receive signals over conventional telephone lines 104, a satellite communication system 106, or using radio frequency (RF) microwave transmission 108. For RF transmission the base station 102 is also in communication with a radiation element 120. The base station sends and receives communication signals via the radiation element 120, which includes an antenna 122 and may also include support electronics 124. Communication signals between the radio base station 102 and the radiation element 120 are generally carried over a coaxial feeder cable 130. Radiation element 120 transmits communication signals from the radio base station to individual clients, as well as receives communication signals from the individual clients and transfers the received signals to the radio base station. Examples of clients, shown in FIG. 1, include mobile wireless handsets such as cell phones 140, mobile laptop computers or PDA 142, and fixed wireless devices such as meter reading equipment 144.
In conventional communication systems each communication channel of the radio base station 102 communicates with a single radiation element 120 device, such as the antenna 122 or the support electronics 124. If a radio base station has multiple communication channels in communication with multiple radiation elements, then there is a separate cable from each communication channel to each radiation element.
FIG. 2 is a block diagram illustrating additional detail of the connection between a radio base station 102 with multiple communication channels and multiple radiation elements 120. As shown in FIG. 2, the base station 102 has six (6) radio frequency (RF) communication channels that are communicated to six (6) radiation elements 120. FIG. 2 illustrates a system that includes an antenna 122 and support electronics at each radiation element 120. To transfer communication signals between the radio base station 102 and the radiation elements 120, six (6) feeder cables 130 connect each of the six (6) communication channels to its individual support electronics 124.
The base station also includes six (6) bias tees 202. The bias tees are used to combine a monitoring signal with the RF communication signal for transmission to the radiation element 120. Typically, the monitoring signal is used to indicate the operational state of a device connected to the feeder 130. The operational state of a device in a conventional communication system is usually monitored by monitoring the current drawn by the device.
For example, in a communication system that has support electronics 124 that include a Mast Head Amplifier (MHA), the MHA draws a specified current when operating in a “normal” mode, for example, 100 mA at 12 VDC. The 100 mA current is supplied by a power supply located in the radio base station and is combined with the RF communication signal in a bias tee 202 at the radio base station. If there is an internal problem with the MHA, for example, a field effect transistor (FET) in the MHA is operating outside normal parameters, the current drawn by the MHA will change to a different value, for example, 150 mA. The change in current drawn by the MHA is as an indication that the MHA has something wrong with it. The change in current drawn by the MHA is detected by the radio base station power supply and an alarm is initiated, signaling that a fault has occurred.
There are several drawbacks to the current monitoring technique for fault detection described above. One of the drawbacks is that only a single device at the radiation element may be attached to the feeder cable 130. If more than one device were connected to the feeder 130 it would not be possible to isolate which device is operating outside its normal operating parameters as indicated by a change in current draw. For example, if there were two MHA devices connected to a single feeder and both drew 100 mA during normal operation, the total current drawn from the radio base station power supply during normal operation would be 200 mA. If one of the MHA had a fault and changed its current draw to 150 mA, the total current drawn from the radio base station power supply would be 250 mA. Thus, it could be determined that one of the MHAs had a fault, but it would not be possible to know which MHA had a fault.
Another drawback to the current monitoring fault detection technique is that it can result in false alarms. For example, if there is a fault in the feeder cable 130, such as a break in the cable and there is no current draw, the radio base station power supply will detect that there is a problem. Thus, it could be determined that there is a problem, but it would not be possible to isolate the fault to one particular element.
To get around the problem described above, conventional communication systems only place one device, such as a MHA, on a feeder cable 130. Using a separate feeder cable 130 for each device solves the problem of isolating the device that has a fault. However, using separate feeders for each device requires additional feeder cables 130 be installed whenever a new device is installed at the radiation element 120.
From the discussion above, it should be apparent that there is a need for a system that can provide for multiple devices to be connected to a feeder cable from a radio base station to a radiation element while allowing detection and isolation of faults within the devices. The present invention fulfills this, and other needs.